Update documentation

CONTRIBUTING.md

@@ -70,14 +70,21 @@ Eg: Object.prototype.toString - '[object Null]' will be returned when
 'this' value is null
 
 #### negative
-**negative**: [regex]
+**negative**: [dictionary containing **phase** and **type**]
 
 This means the test is expected to throw an error of the given type.  If no error is thrown, a test failure is reported.
 
-If an error is thrown, it is implicitly converted to a string.  The second parameter is a regular expression that will be matched against this string.  If the match fails, a test failure is reported.  Thus the regular expression can match either the error name, or the message contents, or both.
+- **type**- If an error is thrown, it is implicitly converted to a string. In order for the test to pass, this value must match the name of the error constructor.
+- **phase** - Negative tests whose **phase** value is "early" must produce the specified error prior to executing code. The value "runtime" dictates that the error is expected to be produced as a result of executing the test code.
 
 For best practices on how to use the negative tag please see Handling Errors and Negative Test Cases, below.
 
+For example:
+
+    negative:
+      phase: early
+      type: ReferenceError
+
 #### es5id
 **es5id**: [es5-test-id]
 
@@ -181,7 +188,9 @@ Expectations for **parsing errors** should be declared using [the `negative` fro
 
 ```javascript
 /*---
-negative: SyntaxError
+negative:
+  phase: early
+  type: SyntaxError
 ---*/
 
 // This `throw` statement guarantees that no code is executed in order to

INTERPRETING.md

@@ -117,20 +117,38 @@ structured as [YAML](http://yaml.org/).
 ### `negative`
 
 These tests are expected to generate an uncaught exception. The value of this
-attribute is the name of the constructor of the expected error. If a test
-configured with the `negative` attribute completes without throwing an
-exception, or if the name of the thrown exception's constructor does not match
-the specified constructor name, the test must be interpreted as "failing."
+attribute is a YAML dictonary with two keys:
+
+- `phase` - the stage of the test interpretation process that the error is
+  expected to be produced; either "early" (meaning, "prior to evaluation") or
+  "runtime" (meaning, "during evaluation"); in the case of "early", additional
+  test transformation may be required--see below
+- `type` - the name of the constructor of the expected error
+
+If a test configured with the `negative` attribute completes without throwing
+an exception, or if the name of the thrown exception's constructor does not
+match the specified constructor name, or if the error occurs at a phase that
+differs from the indicated phase, the test must be interpreted as "failing."
 
 *Example:*
 
 ```js
 /*---
-negative: ReferenceError
+negative:
+  phase: runtime
+  type: ReferenceError
 ---*/
 unresolvable;
 ```
 
+Consumers are free to assert the "early" phase as they see fit.
+
+For example, it is possible to insert a `throw` statement with a unique error
+type at the beginning of the test file. In this case, the statement should be
+inserted *after* the directive desribed in the section titled "Strict Mode"
+(where appropriate), though it must *not* be inserted for tests containing the
+"raw" flag.
+
 ### `includes`
 
 One or more files whose content must be evaluated in the test realm's global